dropdownColor property Null safety

1. flutter_json_widgets
2. widget
3. DropdownButtonFormField
4. dropdownColor property

DropdownButtonFormField class

1. Constructors
2. DropdownButtonFormField
3. fromJson
4. Properties
5. alignment
6. autofocus
7. autovalidateMode
8. borderRadius
9. copyWith
10. decoration
11. disabledHint
12. dropdownColor
13. elevation
14. enableFeedback
15. field
16. focusColor
17. hashCode
18. hint
19. icon
20. iconDisabledColor
21. iconEnabledColor
22. iconSize
23. isDense
24. isExpanded
25. itemHeight
26. items
27. key
28. menuMaxHeight
29. onTap
30. runtimeType
31. style
32. validatorMessages
33. value
34. Methods
35. map
36. mapOrNull
37. maybeMap
38. maybeWhen
39. noSuchMethod
40. toJson
41. toString
42. when
43. whenOrNull
44. Operators
45. operator ==